The influence of strong magnetic fields and instantons on the phase structure of the two-flavor NJL model

TL;DR

This paper investigates how strong magnetic fields influence the phase transitions of quark matter within the two-flavor NJL model, revealing complex behaviors dependent on magnetic field strength and instanton interactions.

Contribution

It provides new insights into the phase structure of quark matter under extreme magnetic fields, considering instanton effects and Landau level occupation.

Findings

Multiple minima with different Landau level occupations can become the global minimum.

Magnetic field and chemical potential significantly alter chiral symmetry breaking.

Phase transition patterns depend on the interplay between magnetic field strength and instanton interactions.

Abstract

Both in heavy-ion collisions as in magnetars very strong magnetic fields are produced, which has its influence on the phases of matter involved. In this paper we investigate the effect of strong magnetic fields (B = 5 m_pi^2 /e = 1.7 x 10^19 G) on the chiral symmetry restoring phase transition using the Nambu-Jona-Lasinio model. It is observed that the pattern of phase transitions depends on the relative magnitude of the magnetic field and the instanton interaction strength. We study two specific regimes in the phase diagram, high chemical potential and zero temperature and vice versa, which are of relevance for neutron stars and heavy-ion collisions respectively. In order to shed light on the behavior of the phase transitions we study the dependence of the minima of the effective potential on the occupation of Landau levels. We observe a near-degeneracy of multiple minima with differing occupation numbers, of which some become the global minimum upon changing the magnetic field or the chemical potential. These minima differ considerably in the amount of chiral symmetry breaking and in some cases also of isospin breaking.